Vibrations transmitted onto payloads in vehicles can cause problems. For example, if the vehicle is an automobile, vibrations cause discomfort. If the vehicle is a space launch vehicle, vibrations can jeopardize the mission. Thus, isolation systems are typically used to isolate a body of the vehicle from the payload to prevent transmission of the vibrations from the body to the payload.
Isolation systems are well known in the art, which include passive systems, semi-active systems, and active systems. Passive systems utilize passive isolating devices such as mounts and shock absorbers to isolate a suspended member from shock and vibration inputs. Passive systems can provide adequate isolation, but usually only dissipate energy from the system.
Semi-active systems have been developed that vary parameters of the isolation system in order to provide better isolation. For example, a semi-active system can incorporate controllable dampers for providing a controllable damper force as needed.
Active systems further control movement of the isolated member in the system by using external power. An example active system is typically used in automobile to control movement of the wheels relative to the chassis or vehicle body, rather than using passive suspension where the movement is determined entirely by the road surface.
With isolation systems, skyhook theory is an idea that all isolation systems are designed to achieve (whether passive, semi-active, or active), which includes having the system maintain a stable posture as if suspended by an imaginary hook in the sky, unaffected by external conditions. Thus, it is a goal of isolation systems to achieve little or no amplification of the system at resonance by adding a force to resist movement of the system. This can be achieved with active systems by implementing a sky-hook isolator that has a feedback link established between the body of the system and the actuator force so that the active control force can be made proportional to the body velocity and that there is no amplification below ωn (where ωn is a natural frequency of the system where the system tends to oscillate in the absence of a damping force).
For a passive system, the skyhook design involves a trade-off between the resonance amplification and the high frequency attenuation. What is needed is a way of achieving isolation performance using passive isolation that is nearly the ideal performance of a skyhook without the need for active isolation and external power.